wlan physical layer

The physical layer of a wireless local area network (WLAN) is responsible for transmitting raw bits over the air between devices. It defines the hardware components and their functions needed to establish and maintain a communication link. The IEEE 802.11 standard specifies the physical layer for WLANs. The physical layer is further divided into two sub-layers: the Physical Layer Convergence Procedure (PLCP) sub-layer and the Physical Medium Dependent (PMD) sub-layer.

1. Physical Layer Convergence Procedure (PLCP) Sub-layer:

a. Preamble:

The PLCP preamble is a set of synchronization and timing information that allows the receiver to lock onto the incoming signal. It includes a short preamble and a long preamble. The short preamble is used for backward compatibility with older standards, while the long preamble provides better performance in terms of synchronization.

b. Header:

The PLCP header contains information about the frame, such as its length, modulation scheme, and other control information. It helps the receiver prepare for the incoming data.

c. Frame Delimiter:

The frame delimiter marks the end of the PLCP header and the beginning of the actual data frame. It helps the receiver distinguish between the header and the data payload.

d. Signal Field:

The signal field contains information about the data rate and modulation scheme to be used for transmission. It helps the receiver configure its parameters accordingly.

2. Physical Medium Dependent (PMD) Sub-layer:

a. Modulation and Encoding:

This part of the PMD sub-layer involves the modulation scheme and error-coding techniques used to transmit data over the air. Common modulation schemes include Binary Phase Shift Keying (BPSK), Quadrature Amplitude Modulation (QAM), and others. Error-coding techniques help in detecting and correcting errors that may occur during transmission.

b. Frequency Bands:

The PMD sub-layer defines the frequency bands used for transmission, such as 2.4 GHz and 5 GHz. The choice of frequency band affects the range, data rate, and susceptibility to interference.

c. Channelization:

Channelization involves dividing the available frequency spectrum into channels to avoid interference between different networks. The IEEE 802.11 standard specifies different channelization schemes, such as the use of 20 MHz or 40 MHz channels.

d. Data Rates:

The physical layer supports multiple data rates. Different modulation and coding schemes are used to achieve varying data rates, allowing the network to adapt to different environmental conditions.

e. Multiple Input Multiple Output (MIMO):

MIMO is a technique where multiple antennas are used for transmission and reception. It improves data rates and reliability by exploiting spatial diversity.

The WLAN physical layer encompasses a set of procedures and techniques for transmitting data over the air, including synchronization, modulation, error coding, and channelization. These elements work together to ensure reliable and efficient wireless communication between devices in a WLAN.